1. Field
Exemplary embodiments relate to audio encoding and decoding, and more particularly, to a method and apparatus for encoding and decoding a high frequency for bandwidth extension.
2. Description of the Related Art
The coding scheme in G.719 is developed and standardized for the purpose of teleconferencing and performs a frequency domain transform by performing a modified discrete cosine transform (MDCT) to directly code an MDCT spectrum for a stationary frame and change a time domain aliasing order for a non-stationary frame so as to consider temporal characteristics. A spectrum obtained for a non-stationary frame may be constructed in a similar form to a stationary frame by performing interleaving to construct a codec with the same framework as the stationary frame. Energy of the constructed spectrum is obtained, normalized, and quantized. In general, energy is represented as a root mean square (RMS) value, and from a normalized spectrum, the number of bits required for each band is calculated through energy-based bit allocation, and a bitstream is generated through quantization and lossless coding based on information regarding the bit allocation for each band.
According to the decoding scheme in G.719, as a reverse process of the coding scheme, a normalized dequantized spectrum is generated by dequantizing energy from a bitstream, generating bit allocation information based on the dequantized energy, and dequantizing a spectrum. When bits are insufficient, a dequantized spectrum may not exist in a specific band. To generate noise for the specific band, a noise filling method for generating noise according to a transmitted noise level by generating a noise codebook based on a dequantized spectrum of a low frequency is applied. For a band of a specific frequency or higher, a bandwidth extension scheme for generating a high frequency signal by folding a low frequency signal is applied.